What are Machining Tolerances?

In manufacturing specific parts, tolerances are crucial indicators of the required level of precision. Simply put, machining tolerances denote the extent to which a part's final dimensions or measured values can vary.

Machinists quantify machining tolerances using numerical values, typically preceded by a ± symbol. For instance, you might assign a tolerance of ±0.001 inches to a part that measures 2.550 inches in length. This means the manufactured part's length can fluctuate between 2.549 and 2.551 inches. If a part with a height of 1.5 inches requires a tolerance of ±0.005 inches, the final part must fall within the range of 1.495 and 1.505 inches to pass quality inspection.

Specified machining tolerances inform manufacturers and CNC machining services about the level of precision needed when producing a part. The smaller the tolerance—referred to as a tighter tolerance in the manufacturing world—the higher the precision required. Conversely, with a larger tolerance—also known as a looser tolerance—less precision is necessary. This distinction is paramount.